Complete foundational data layer with repository implementation

- Add GORM dependencies for SQLite and PostgreSQL
- Create domain models (User, Session, File) with common errors
- Implement repository interfaces and database layer with migrations
- Update WebApp to bootstrap with database and repositories
- Add comprehensive unit tests for repository methods
- Update config structure to support multiple database drivers
- Extend AGENTS.md with debugging principles and dependency rules

internal/config/config.go

@@ -20,8 +20,22 @@ type ServerConfig struct {
 }
 
 type DatabaseConfig struct {
-	Driver string `mapstructure:"driver"`
-	Path   string `mapstructure:"path"`
+	Driver   string         `mapstructure:"driver"`
+	SQLite   SQLiteConfig   `mapstructure:"sqlite"`
+	Postgres PostgresConfig `mapstructure:"postgres"`
+}
+
+type SQLiteConfig struct {
+	Path string `mapstructure:"path"`
+}
+
+type PostgresConfig struct {
+	Host     string `mapstructure:"host"`
+	Port     int    `mapstructure:"port"`
+	User     string `mapstructure:"user"`
+	Password string `mapstructure:"password"`
+	DBName   string `mapstructure:"dbname"`
+	SSLMode  string `mapstructure:"sslmode"`
 }
 
 type StorageConfig struct {
@@ -60,8 +74,26 @@ func (c *Config) Validate() error {
 		errs = append(errs, fmt.Errorf("server.host: %q is not a valid IP address", c.Server.Host))
 	}
 
-	if c.Database.Path == "" {
-		errs = append(errs, errors.New("database.path: must not be empty"))
+	switch c.Database.Driver {
+	case "sqlite3":
+		if c.Database.SQLite.Path == "" {
+			errs = append(errs, errors.New("database.sqlite.path: must not be empty"))
+		}
+	case "postgres":
+		if c.Database.Postgres.Host == "" {
+			errs = append(errs, errors.New("database.postgres.host: must not be empty"))
+		}
+		if c.Database.Postgres.Port < 1 || c.Database.Postgres.Port > 65535 {
+			errs = append(errs, fmt.Errorf("database.postgres.port: %d out of range [1, 65535]", c.Database.Postgres.Port))
+		}
+		if c.Database.Postgres.User == "" {
+			errs = append(errs, errors.New("database.postgres.user: must not be empty"))
+		}
+		if c.Database.Postgres.DBName == "" {
+			errs = append(errs, errors.New("database.postgres.dbname: must not be empty"))
+		}
+	default:
+		errs = append(errs, fmt.Errorf("database.driver: %q is not supported (use sqlite3 or postgres)", c.Database.Driver))
 	}
 
 	if c.Storage.Local.Path == "" {

internal/config/load.go

@@ -13,7 +13,13 @@ func defaults(v *viper.Viper) {
 	v.SetDefault("server.port", 10086)
 
 	v.SetDefault("database.driver", "sqlite3")
-	v.SetDefault("database.path", "data/mygo.db")
+	v.SetDefault("database.sqlite.path", "data/mygo.db")
+	v.SetDefault("database.postgres.host", "localhost")
+	v.SetDefault("database.postgres.port", 5432)
+	v.SetDefault("database.postgres.user", "mygo")
+	v.SetDefault("database.postgres.password", "")
+	v.SetDefault("database.postgres.dbname", "mygo")
+	v.SetDefault("database.postgres.sslmode", "disable")
 
 	v.SetDefault("storage.driver", "local")
 	v.SetDefault("storage.local.path", "data/files")

internal/config/load_test.go

@@ -22,7 +22,7 @@ func TestDefaults(t *testing.T) {
 		{"server.host", cfg.Server.Host, "0.0.0.0"},
 		{"server.port", cfg.Server.Port, 10086},
 		{"database.driver", cfg.Database.Driver, "sqlite3"},
-		{"database.path", cfg.Database.Path, "data/mygo.db"},
+		{"database.sqlite.path", cfg.Database.SQLite.Path, "data/mygo.db"},
 		{"storage.driver", cfg.Storage.Driver, "local"},
 		{"storage.local.path", cfg.Storage.Local.Path, "data/files"},
 		{"jwt.access_ttl", cfg.JWT.AccessTTL, "15m"},
@@ -49,7 +49,8 @@ server:
 
 database:
     driver: sqlite3
-    path: /tmp/mygo.db
+    sqlite:
+        path: /tmp/mygo.db
 
 storage:
     driver: local
@@ -77,8 +78,8 @@ jwt:
 	if cfg.Server.Port != 9090 {
 		t.Errorf("server.port = %d, want %d", cfg.Server.Port, 9090)
 	}
-	if cfg.Database.Path != "/tmp/mygo.db" {
-		t.Errorf("database.path = %q, want %q", cfg.Database.Path, "/tmp/mygo.db")
+	if cfg.Database.SQLite.Path != "/tmp/mygo.db" {
+		t.Errorf("database.sqlite.path = %q, want %q", cfg.Database.SQLite.Path, "/tmp/mygo.db")
 	}
 	if cfg.Storage.Local.Path != "/tmp/mygo-storage" {
 		t.Errorf("storage.local.path = %q, want %q", cfg.Storage.Local.Path, "/tmp/mygo-storage")
@@ -98,7 +99,7 @@ func TestEnvOverride(t *testing.T) {
 	t.Setenv("MYGO_SERVER_PORT", "8080")
 	t.Setenv("MYGO_SERVER_HOST", "192.168.1.1")
 	t.Setenv("MYGO_JWT_SECRET", "env-secret")
-	t.Setenv("MYGO_DATABASE_PATH", "/env/path/db.sqlite")
+	t.Setenv("MYGO_DATABASE_SQLITE_PATH", "/env/path/db.sqlite")
 
 	v := New()
 	cfg, err := Load(v, "")
@@ -115,8 +116,8 @@ func TestEnvOverride(t *testing.T) {
 	if cfg.JWT.Secret != "env-secret" {
 		t.Errorf("jwt.secret = %q, want %q", cfg.JWT.Secret, "env-secret")
 	}
-	if cfg.Database.Path != "/env/path/db.sqlite" {
-		t.Errorf("database.path = %q, want %q", cfg.Database.Path, "/env/path/db.sqlite")
+	if cfg.Database.SQLite.Path != "/env/path/db.sqlite" {
+		t.Errorf("database.sqlite.path = %q, want %q", cfg.Database.SQLite.Path, "/env/path/db.sqlite")
 	}
 }